The present invention relates generally to clutches, and more particularly to viscous clutches.
Viscous clutches are used in a wide variety of automotive fan drive applications, among other uses. These clutches typically employ relatively thick silicone oil (more generally called shear fluid or viscous fluid) for the selective transmission of torque between two rotatable components. It is possible to engage or disengage the clutch by selectively allowing the oil into and out of a working area of the clutch located between input and output members (e.g., between an input rotor and an output housing). A valve is used to control the flow of the oil in the working area between the input and the output. Recent clutch designs have been employed that allow the oil to be stored in a reservoir attached to an input rotor while the clutch is disengaged, in order to keep kinetic energy available in the oil to allow rapid engagement of the clutch from the off condition. This also allows the clutch to have a very low output speed (e.g., fan speed) while the valve is positioned to obstruct oil flow into the working area. However, attachment of the reservoir to the rotor disk substantially limits design flexibility. For instance, many prior art clutches have limitations associated with magnetic flux circuits used for control of the valve, and positioning a valve relative to a rotating reservoir while still providing suitable fluid and flux paths presents formidable challenges. These constraints typically apply while still seeking to provide a relatively compact and low-mass clutch package that can still accommodate desired torque loads and function quickly, efficiently and reliably.
Therefore, it is desired to provide an alternative viscous clutch.